Thermosetting resin composition, prepreg, fiber-reinforced plastic molded body and method for producing same

ABSTRACT

A thermosetting resin composition (C) of which curing can be started at a relatively low temperature in a short time and a cured product exhibits high heat resistance, the thermosetting resin composition (C) comprising an epoxy resin; an epoxy resin curing agent; and an epoxy resin curing accelerator, wherein the epoxy resin curing agent contains an imidazole-based curing agent 1 which is not encapsulated in a microcapsule and a curing agent 2 which is encapsulated in a microcapsule, and the epoxy resin curing accelerator comprises a urea derivative.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuing application based on U.S. applicationSer. No. 16/281,298, filed Feb. 21, 2019, and published as US2019/0185612 A1, which was bypass continuation application ofPCT/JP2017/030950, filed on Aug. 29, 2017, claiming the benefit ofpriority date of Japanese Appl. No. 2016-166878, filed Aug. 29, 2016,the entire content of each which is incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a thermosetting resin composition, aprepreg, a fiber-reinforced plastic molded body and a method forproducing the same.

BACKGROUND ART

Fiber-reinforced plastic molded bodies containing a reinforcing fibersubstrate and a matrix resin composition are widely used in industrialapplications and the like such as aircraft and motor vehicles because ofexcellent mechanical properties and the like, and the application rangethereof has been extended more and more in recent years. For example, afiber-reinforced plastic molded body, formed by heating and pressurizinga prepreg laminate obtained by laminating a plurality of sheet-likeprepreg substrates in which a reinforcing fiber substrate is impregnatedwith a matrix resin composition, is known.

As the reinforcing fiber substrate, a glass fiber or a carbon fiber isoften used.

As a matrix resin composition, a thermosetting resin compositioncontaining a phenol resin, a melamine resin, a bismaleimide resin, anunsaturated polyester resin, an epoxy resin or the like is often usedfrom the viewpoint of excellent impregnating property and heatresistance. Among these, an epoxy resin composition is widely used sincea fiber-reinforced plastic molded body which exhibits excellent heatresistance and moldability and has a higher mechanical strength isobtained.

In addition, as a fiber-reinforced plastic molded body, afiber-reinforced plastic molded body which is molded by being heated andpressurized in a state in which a resin film containing a reinforcingfiber and a thermosetting resin composition is further laminated on thesurface of a prepreg laminate for the purpose of suppressing aphenomenon that the fibers present in the vicinity of the surface areseen through (that is, preventing a phenomenon that the fibers are notsufficiently buried in the resin layer but are exposed) is known. Such aresin film has a higher proportion of thermosetting resin compositionand a lower proportion of reinforcing fiber than the prepreg substrate.

As a method for producing a fiber-reinforced plastic molded body, forexample, a method using an autoclave (JP H10-128778 A), a method using avacuum bag (JP 2002-159613 A), a compression molding method (JPH10-95048 A), and the like are known. However, in these methods, it isrequired to heat the prepreg laminate at 160° C. or higher for aboutfrom 2 to 6 hours until the prepreg laminate is cured when curing theprepreg laminate through heating and pressurization and thus the energyconsumption is great and the productivity is low.

As a molding method to be frequently used in motor vehicle applications,high cycle press molding is known (WO 2004/048435 A). In the high cyclepress molding, curing is conducted at about 100° C. to 150° C. under ahigh pressure in a short time of about from several minutes to severaltens of minutes in order to achieve mass production of products.

However, in a case in which molding is conducted by laminating a resinfilm on the surface of a prepreg laminate, the thermosetting resincomposition in the vicinity of the surface excessively flows out fromthe edge portion of the mold in some cases as the viscosity of thethermosetting resin composition contained in the resin film decreases byan increase in the temperature under a high pressure. As describedabove, when the thermosetting resin composition on the surfaceexcessively flows out of the mold, molding appearance defects aregenerated that the fibers are exposed by resin withering or fibermeandering due to excessive flow of resin on the surface of a moldedbody to be obtained. In this case, and a case in which the heatresistance of the thermosetting resin composition contained in the resinfilm on the surface is not sufficiently high, the molded body absorbsmoisture with the elapse of time even being painted and streaky paintingappearance defects are generated on the surface of the molded body bythe relaxation of residual stress of the molded body when heat isapplied.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a thermosetting resincomposition of which curing can be started at a relatively lowtemperature in a short time and a cured product exhibits high heatresistance and a prepreg to be obtained by impregnating a reinforcingfiber substrate with this thermosetting resin composition.

Another object of the present invention is to provide a fiber-reinforcedplastic molded body which can suppress excessive flow of the resin atthe time of heat and pressure treatment, in which the generation ofappearance defects at molding such as resin withering and fibermeandering on the surface and a defect that fibers are seen through thesurface are suppressed, and which exhibits excellent molding appearanceand painting appearance, for example, even in the case of beingsubjected to high cycle press molding or being exposed to a wet heatcondition by using a resin film to be obtained using the thermosettingresin composition of the present invention, and a method for producingthe same.

[1] A thermosetting resin composition (C) containing an epoxy resin, anepoxy resin curing agent, and an epoxy resin curing accelerator, inwhich the epoxy resin curing agent contains an imidazole-based curingagent 1 which is not encapsulated in a microcapsule and a curing agent 2which is encapsulated in a microcapsule, and the epoxy resin curingaccelerator contains a urea derivative.

[2] The thermosetting resin composition (C) according to [1], in whichthe imidazole-based curing agent 1 is an imidazole-based curing agent 1represented by the following Formula (1):

where R¹ represents a linear or branched alkyl group having from 1 to 5carbon atoms which may have a substituent, a phenyl group which may havea substituent, a hydrogen atom, or a hydroxymethyl group and R²represents a linear or branched alkyl group having from 1 to 5 carbonatoms, a phenyl group which may have a substituent, or a hydrogen atom.

[3] The thermosetting resin composition (C) according to [1] or [2], inwhich the urea derivative is 3-phenyl-1,1-dimethylurea or2,4-bis(3,3-dimethylureido)toluene.

[4] The thermosetting resin composition (C) according to any one of [1]to [3], in which the imidazole-based curing agent 1 is2-phenyl-4,5-dihydroxymethylinidazole or2-phenyl-4-methyl-5-hydroxymethylimidazole.

[5] The thermosetting resin composition (C) according to any one of [1]to [4], in which the curing agent 2 which is encapsulated in amicrocapsule contains an imidazole derivative represented by thefollowing Formula (2):

where R³ represents an organic group containing one or more carbon atomsand R⁴ to R⁶ are the same as or different from one another and eachrepresent a hydrogen atom, a methyl group, or an ethyl group).

[6] The thermosetting resin composition (C) according to any one of [1]to [5], in which the epoxy resin contains an epoxy resin having astructure represented by the following Formula (3) in a molecule and/ora bisphenol A type epoxy resin:

[7] The thermosetting resin composition (C) according to any one of [1]to [6], in which a content of the imidazole-based curing agent 1 in thethermosetting resin composition (C) is from 5% to 15% by mass, a contentof the curing agent 2 which is encapsulated in a microcapsule is from 1%to 3% by mass, and a content of the urea derivative is from 2% to 5% bymass.

[8] A thermosetting resin composition (C), in which the thermosettingresin composition (C) has a lowest viscosity at from 80° C. to 98° C. intemperature-programmed viscosity measurement to be conducted underconditions of an initial temperature of 30° C. and a rate of temperatureincrease of 2.0° C./min and a glass transition temperature of a curedproduct to be obtained by heating the thermosetting resin composition(C) at 140° C. for 5 minutes to be attained by dynamic viscoelasticitymeasurement is 150° C. or higher.

[9] A prepreg containing a reinforcing fiber substrate impregnated withthe thermosetting resin composition (C) according to any one of [1] to[8].

[10] The prepreg according to [9], in which the reinforcing fibersubstrate is a glass fiber.

[11] The prepreg according to [9], in which the reinforcing fibersubstrate is a carbon fiber.

[12] A method for producing a fiber-reinforced plastic molded body,including: producing a film laminate (F) by laminating a resin filmformed using a thermosetting resin composition (C) on at least onesurface of a prepreg laminate (E) obtained by laminating a plurality ofsheet-like prepreg substrates formed by impregnating a reinforcing fibersubstrate (A) with a thermosetting resin composition (B); and subjectingthe obtained laminate to a heat and pressure treatment using a mold, inwhich the thermosetting resin composition (C) is the thermosetting resincomposition (C) described in [1] to [8].

[13] The method for producing a fiber-reinforced plastic molded bodyaccording to [12], in which the resin film contains a reinforcing fibersubstrate (D) having a fiber areal weight of 50 g/m² or less.

[14] The method for producing a fiber-reinforced plastic molded bodyaccording to [12] or [13], in which the reinforcing fiber substrate (D)is a nonwoven fabric formed of a reinforcing fiber.

[15] The method for producing a fiber-reinforced plastic molded bodyaccording to any one of [12] to [14], in which a preform is produced byshaping the film laminate (F) obtained in the production of the filmlaminate (F) and the preform used as the laminate is subjected to a heatand pressure treatment using a mold.

[16] A fiber-reinforced plastic molded body which is a cured product ofthe film laminate (F) according to [13] or [14] or the preform accordingto [15].

[17] A fiber-reinforced plastic molded body which is a cured product ofthe prepreg according to any one of [9] to [11].

According to the present invention, a thermosetting resin composition ofwhich curing can be started at a relatively low temperature in a shorttime and a cured product exhibits high heat resistance and a prepreg tobe obtained by impregnating a reinforcing fiber substrate with thisthermosetting resin composition are provided.

According to the present invention, a fiber-reinforced plastic moldedbody which can suppress excessive flow of the resin at the time of heatand pressure treatment, in which the generation of molding appearancedefects such as resin withering and fiber meandering on the surface anda defect that fibers are seen through the surface are suppressed, andwhich exhibits excellent molding appearance and painting appearance, forexample, even in the case of being subjected to high cycle press moldingor being exposed to a wet heat condition by using a resin film to beobtained using the thermosetting resin composition of the presentinvention, and a method for producing the same are also provided.

BRIEF DESCRIPTION OF DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view illustrating an example of a laminateto be used in a method for producing a fiber-reinforced plastic moldedbody of the present invention:

FIG. 2 is a cross-sectional view illustrating an example of a moldingstep in a method for producing a fiber-reinforced plastic molded body ofthe present invention; and

FIG. 3 is a cross-sectional view illustrating an example of afiber-reinforced plastic molded body of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed, but the present invention is not limited only to theseembodiments.

<Thermosetting Resin Composition (C)>

The thermosetting resin composition (C) of the present inventioncontains an epoxy resin, an epoxy resin curing agent, and an epoxy resincuring accelerator, and in the thermosetting resin composition (C), theepoxy resin curing agent contains an imidazole-based curing agent 1which is not encapsulated in a microcapsule and a curing agent 2 whichis encapsulated in a microcapsule and the epoxy resin curing acceleratorcontains a urea derivative.

By using the imidazole-based curing agent 1 which is not encapsulated ina microcapsule, it is possible to increase the temperature for reactioninitiation. It is thus possible to increase the glass transitiontemperature of cured product to be attained by dynamic viscoelasticitymeasurement.

By using the curing agent 2 which is encapsulated in a microcapsule, itis possible to achieve both stability and fast curability of thethermosetting resin composition.

In addition, it is possible to quickly cure the thermosetting resincomposition since the urea derivative has an effect of acceleratingcuring at a relatively low temperature.

In the thermosetting resin composition (C) of the present invention, thetemperature at which the lowest viscosity is attained is preferably from80° C. to 98° C., more preferably from 85° C. to 97° C., and still morepreferably from 90° C. to 95° C. in the temperature-programmed viscositymeasurement in which the initial temperature is set to 30° C. and thetemperature is increased at 2.0° C./min.

By concurrently using the curing agent 2 which is encapsulated in amicrocapsule and the urea derivative, it is possible to achieve theabove property.

When the temperature at which the lowest viscosity is attained in thetemperature-programmed viscosity measurement described above is in theabove range, the amount of the thermosetting resin composition (C)flowing at the time of molding is likely to be suppressed in a properrange. When the temperature at which the lowest viscosity is attained inthe temperature-programmed viscosity measurement described above isequal to or higher than the lower limit value, the amount of thethermosetting resin composition (C) flowing at the time of molding isnot too small and the thermosetting resin composition (C) is likely tospread to every corner of the molding mold. When the temperature atwhich the lowest viscosity is attained in the temperature-programmedviscosity measurement described above is equal to or lower than theupper limit value, excessive flow of the thermosetting resin composition(C) at the time of molding is likely to be suppressed and moldingappearance defects such as concave and convex on the surface of themolded body is less likely to occur, the fiber is less likely to beexposed by resin withering, or the fiber meandering due to excessiveflow of resin is less likely to occur.

It is preferable that the glass transition temperature of a curedproduct to be obtained by heating the thermosetting resin composition(C) of the present invention at 140° C. for 5 minutes to be attained bydynamic viscoelasticity measurement is 150° C. or higher.

By concurrently using the imidazole-based curing agent 1 which is notencapsulated in a microcapsule and the curing agent 2 which isencapsulated in a microcapsule, it is possible to achieve the aboveproperty.

When the glass transition temperature in the dynamic viscoelasticitymeasurement described above is equal to or higher than the lower limitvalue, appearance defects are less likely to be generated even whenmoisture absorption and heating and cooling are repeated under theconditions of use after the cured product has been painted. The glasstransition temperature is more preferably 152° C. or higher.

When curing the thermosetting resin composition (C) in the dynamicviscoelasticity measurement described above, there is a method in whichthe thermosetting resin composition (C) is sandwiched between glassplates and heated in an oven or a method in which the resin is placed ina preheated mold and the mold is closed and heated. As the curing time,curing is conducted for 5 minutes after the temperature of the glassplate or mold which is in contact with the resin has reached 140° C.

In other words, in the case of a method in which the thermosetting resincomposition (C) is sandwiched between glass plates and heated in anoven, the thermosetting resin composition (C) is sandwiched betweenglass plates, placed in an oven at 140° C., heating is stopped when 5minutes elapses after the temperature of the glass plate has reached140° C., and the cured product is take out from the oven. In addition,in a method in which the resin is placed in a preheated mold and themold is closed and heated, the resin is poured into a mold heated to140° C., the mold is immediately closed and held at 140° C., the mold isopened after 5 minutes, and the cured product is taken out from themold.

The glass transition point of the cured product is determined by amethod to be described later because of the temperature dependency ofthe shear storage modulus (G′) of the cured product to be attained bydynamic viscoelasticity measurement.

It is preferable that the thermosetting resin composition (C) of thepresent invention has the lowest viscosity at from 80° C. to 98° C. inthe temperature-programmed viscosity measurement to be conducted underconditions of an initial temperature of 30° C. and a rate of temperatureincrease of 2.0° C./min and the glass transition temperature of a curedproduct to be obtained by heating the thermosetting resin composition(C) at 140° C. for 5 minutes to be attained by the dynamicviscoelasticity measurement is 150° C. or higher.

When the temperature at which the lowest viscosity is attained in thetemperature-programmed viscosity measurement and the glass transitiontemperature of the cured product to be attained by the dynamicviscoelasticity measurement are in the above ranges, it is possible tosuppress the molding defects and appearance defects described above.

These properties can be achieved by using the imidazole-based curingagent 1 which is not encapsulated in a microcapsule, the curing agent 2which is encapsulated in a microcapsule, and the urea derivativeconcurrently.

The viscosity of the thermosetting resin composition (C) of the presentinvention at 30° C. is preferably from 1.0□102 to 1.0□105 Pa·s, morepreferably 5.0□102 to 9.8□104 Pa·s, and still more preferably 1.0×10³ to9.7×10⁴ Pa·s.

The viscosity of the thermosetting resin composition (C) at 30° C. canbe mainly achieved by adjusting the ratio of an epoxy resin which isliquid at room temperature to an epoxy resin which is solid at roomtemperature.

When the viscosity of the thermosetting resin composition (C) at 30° C.is in the above range, the shape of the prepreg of the present inventionis easily maintained.

In addition, when the viscosity of the thermosetting resin composition(C) at 30° C. is equal to or higher than the lower limit value, a resinfilm formed using the thermosetting resin composition (C) exhibitsexcellent handling properties and work such as fabrication andlamination of the resin film and molding is facilitated. When theviscosity of the thermosetting resin composition (C) at 30° C. is equalto or lower than the upper limit value, a reinforcing fiber substrate(D) to be described later or a reinforcing fiber substrate is easilyimpregnated with the thermosetting resin composition (C) at the time offabrication of a resin film containing the reinforcing fiber substrate(D) and at the time of fabrication of the prepreg of the presentinvention, excessive heating is not required at the time ofimpregnation, and the draping property of the resin film is also hardlyimpaired.

The lowest viscosity in the temperature-programmed viscosity measurementis preferably from 0.5 Pa·s to 50 Pa·s, more preferably from 1 Pa·s to10 Pa·s, and still more preferably from 2 Pa·s to 5 Pa·s.

When the lowest viscosity in the temperature-programmed viscositymeasurement is in the above range, molding appearance defects are hardlygenerated. When the lowest viscosity in the temperature-programmedviscosity measurement is equal to or higher than the lower limit value,excessive flow of the thermosetting resin composition (C) is likely tobe suppressed and appearance defects such as concave and convex arehardly generated on the surface of the molded body. When the lowestviscosity in the temperature-programmed viscosity measurement is equalto or lower than the upper limit value, the thermosetting resincomposition (C) is likely to spread to every corner of the mold at thetime of molding and molded body having favorable appearance is likely tobe obtained.

(Epoxy Resin)

Examples of the epoxy resin to be contained in the thermosetting resincomposition (C) of the present invention may include a compound havingtwo or more epoxy groups in the molecule.

As the examples of the epoxy resin, a glycidyl ether type epoxy resin tobe obtained from a compound having a hydroxyl group in the molecule andepichlorohydrin, a glycidyl amine type epoxy resin to be obtained from acompound having an amino group in the molecule and epichlorohydrin, aglycidyl ester type epoxy resin to be obtained from a compound having acarboxyl group in the molecule and epichlorohydrin, an alicyclic epoxyresin to be obtained by oxidizing a compound having a double bond in themolecule, an epoxy resin having a heterocyclic structure, or an epoxyresin in which two or more kinds of groups to be selected from these aremixed in the molecule is used.

In addition, as an epoxy resin other than these, an epoxy resin having astructure represented by Formula (3) above in the molecule can also beused.

[Glycidyl Ether Type Epoxy Resin]

Specific examples of the glycidyl ether type epoxy resin may includearyl glycidyl ether type epoxy resins such as a bisphenol A type epoxyresin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, aresorcinol type epoxy resin, a phenol novolak type epoxy resin, atrisphenol novolak type epoxy resin, a naphthalene type epoxy resin, andan anthracene type epoxy resin; a polyethylene glycol type epoxy resin,a polypropylene glycol type epoxy resin, a dicyclopentadiene type epoxyresin, and positional isomers thereof and substitution products thereofwith an alkyl group and halogen.

Examples of commercially available products of a bisphenol A type epoxyresin may include EPON 825, jER 826, jER 827, and jER 828 (allmanufactured by Mitsubishi Chemical Corporation), EPICLON (registeredtrademark) 850 (manufactured by DIC Corporation), Epototo (registeredtrademark) YD-128 (manufactured by NIPPON STEEL & SUMIKIN CHEMICAL CO.,LTD.), DER-331 and DER-332 (all manufactured by The Dow ChemicalCompany), and Bakelite EPR 154, Bakelite EPR 162, Bakelite EPR 172,Bakelite EPR 173, and Bakelite EPR 174 (all manufactured by BakeliteGmbH).

Examples of commercially available products of a bisphenol F type epoxyresin may include jER 806, jER 807, and jER 1750 (all manufactured byMitsubishi Chemical Corporation), EPICLON (registered trademark) 830(manufactured by DIC Corporation), and Epototo (registered trademark)YD-170 and Epototo (registered trademark) YD-175 (all manufactured byNIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.), Bakelite EPR 169(manufactured by Bakelite GmbH), and GY 281, GY 282, and GY 285 (allmanufactured by Huntsman Advanced Materials LLC).

Examples of commercially available products of a bisphenol S type epoxyresin may include EPICLON (registered trademark) EXA-1514 (manufacturedby DIC Corporation).

Examples of commercially available products of a resorcinol type epoxyresin may include DENACOL (registered trademark) EX-201 (manufactured byNagase ChemteX Corporation).

Examples of commercially available products of a phenol novolak typeepoxy resin may include jER 152 and jER 154 (all manufactured byMitsubishi Chemical Corporation), EPICLON (registered trademark) 740(manufactured by DIC Corporation), and EPN 179 and EPN 180 (manufacturedby Huntsman Advanced Materials LLC).

Examples of commercially available products of a trisphenolmethane typeepoxy resin may include TACTIX (registered trademark) 742 (manufacturedby Huntsman Advanced Materials LLC), EPPN 501H, EPPN 501HY, EPPN 502H,and EPPN 503H (all manufactured by Nippon Kayaku Co., Ltd.), and jER1032H60 (manufactured by Mitsubishi Chemical Corporation).

Examples of commercially available products of a naphthalene type epoxyresin may include HP-4032 and HP-4700 (manufactured by DIC Corporation)and NC-7300 (manufactured by Nippon Kayaku Co., Ltd.).

Examples of commercially available products of a dicyclopentadiene typeepoxy resin may include XD-100 (manufactured by Nippon Kayaku Co., Ltd.)and HP 7200 (manufactured by DIC Corporation).

Examples of commercially available products of an anthracene type epoxyresin may include YL7172YX-8800 (manufactured by Mitsubishi ChemicalCorporation).

As the glycidyl ether type epoxy resin, a bisphenol A type epoxy resinis preferable.

[Glycidyl Amine Type Epoxy Resin]

Specific examples of the glycidyl amine type epoxy resin may includetetraglycidyl diaminodiphenylmethanes, a glycidyl compound ofaminophenol, a glycidyl compound of aminocresol, glycidylanilines, and aglycidyl compound of xylenediamine.

Examples of commercially available products of tetraglycidyldiaminodiphenylmethanes may include SUMI-EPOXY (registered trademark)ELM-434 (manufactured by Sumitomo Chemical Company, Limited), ARALDITE(registered trademark) MY 720, ARALDITE (registered trademark) MY 721,ARALDITE (registered trademark) MY 9512, ARALDITE (registered trademark)MY 9612, ARALDITE (registered trademark) MY 9634, and ARALDITE(registered trademark) MY 9663 (all manufactured by Huntsman AdvancedMaterials LLC), jER 604 (manufactured by Mitsubishi ChemicalCorporation), and Bakelite EPR 494, Bakelite EPR 495, Bakelite EPR 496,and Bakelite EPR 497 (all manufactured by Bakelite GmbH).

Examples of commercially available products of a glycidyl compound ofaminophenol and a glycidyl compound of aminocresol may include jER 630(manufactured by Mitsubishi Chemical Corporation), ARALDITE (registeredtrademark) MY 0500, ARALDITE (registered trademark) MY 0510, andARALDITE (registered trademark) MY 0600 (all manufactured by HuntsmanAdvanced Materials LLC), and SUMI-EPOXY (registered trademark) ELM 120and SUMI-EPOXY (registered trademark) ELM 100 (all manufactured bySumitomo Chemical Company, Limited).

Examples of commercially available products of glycidylanilines mayinclude GAN and GOT (Nippon Kayaku Co., Ltd.) and Bakelite EPR 493(manufactured by Bakelite GmbH).

Examples of a glycidyl compound of xylenediamine may include TETRAD(registered trademark)-X (manufactured by MITSUBISHI GAS CHEMICALCOMPANY, INC.).

[Glycidyl Ester Type Epoxy Resin]

Specific examples of the glycidyl ester type epoxy resin may includephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester,isophthalic acid diglycidyl ester, dimer acid diglycidyl ester, andisomers thereof.

Examples of commercially available products of phthalic acid diglycidylester may include Epomic (registered trademark) R508 (manufactured byMitsui Chemicals, Inc.) and DENACOL (registered trademark) EX-721(manufactured by Nagase ChemteX Corporation).

Examples of commercially available products of hexahydrophthalic aciddiglycidyl ester may include Epomic (registered trademark) R540(manufactured by Mitsui Chemicals, Inc.) and AK-601 (manufactured byNippon Kayaku Co., Ltd.).

Examples of commercially available products of dimer acid diglycidylester may include jER 871 (manufactured by Mitsubishi ChemicalCorporation) and Epototo (registered trademark) YD-171 (manufactured byNIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.).

[Alicyclic Epoxy Resin]

Specific examples of the alicyclic epoxy resin may include a compoundhaving a 1,2-epoxycyclohexane ring as a partial structure.

Examples of commercially available products of a compound having a1,2-epoxycyclohexane ring as a partial structure may include CELLOXIDE(registered trademark) 2021P, CELLOXIDE (registered trademark) 2081, andCELLOXIDE (registered trademark) 3000 (all manufactured by DaicelCorporation) and CY 179 (manufactured by Huntsman Advanced MaterialsLLC).

[Epoxy Resin Having Heterocyclic Structure]

Specific examples of the epoxy resin having a heterocyclic structure mayinclude a compound having an oxazolidone ring as a partial structure anda compound having a xanthene skeleton as a partial structure.

Examples of commercially available products of a compound having anoxazolidone ring as a partial structure may include AER 4152, AER 4151,LSA 4311, LSA 4313, and LSA 7001 (all manufactured by Asahi KaseiE-materials Corporation).

Examples of commercially available products of a compound having axanthene skeleton as a partial structure may include EXA-7335(manufactured by DIC Corporation).

[Epoxy Resin Having Structure Represented by Formula (3) in Molecule]

Examples of the epoxy resin having a structure represented by thefollowing Formula (3) in the molecule may include a reaction product ofan epoxy resin with an amine compound having at least one sulfur atom inthe molecule.

Examples of the amine compound having at least one sulfur atom in themolecule may include 4,4′-diaminodiphenylsulfone,3,3′-diaminodiphenylsulfone, bis(4-(4-aminophenoxy)phenyl)sulfone,bis(4-(3-aminophenoxy)phenyl)sulfone, and any derivative thereof.

Among these, it is preferable to use diaminodiphenylsulfone and it ismore preferable to use 4,4′-diaminodiphenylsulfone from the viewpoint ofheat resistance of the cured resin.

In addition, examples of the epoxy resin which reacts with an aminecompound having at least one sulfur atom in the molecule to form anepoxy resin having a structure represented by Formula (3) above in themolecule may include bisphenol type epoxy resins such as a bisphenol Atype epoxy resin and a bisphenol F type epoxy resin, but a bisphenol Atype epoxy resin is preferable among these.

Examples of a method for obtaining the epoxy resin having a structurerepresented by Formula (3) may include a method in which an epoxy resinis mixed with an amine compound having at least one sulfur atom in themolecule, specifically, an amine compound having a structure representedby Formula (3) at a mass ratio of from 100:3 to 100:30, preferably from100:5 to 100:20 and the mixture is heated at from 130° C. to 200° C.,preferably from 140° C. to 170° C. for reaction. In the case of usingthis method, the unreacted epoxy resin and the amine compound remain inthe reaction product in some cases, but it is not particularly requiredto remove these residues.

It is preferable to use an epoxy resin having a structure represented byFormula (3) above in the molecule as the epoxy resin to be contained inthe thermosetting resin composition (C) of the present invention sinceit is possible to easily adjust the viscosity of the thermosetting resincomposition (C).

In other words, it is possible to control the viscosity of the reactionproduct to be obtained high by adjusting the conditions of the reactionof the epoxy resin with the amine compound having at least one sulfuratom in the molecule, for example, by increasing the reactiontemperature and the reaction time, and it is possible to control theviscosity of the reaction product to be obtained low by decreasing thereaction temperature and the reaction time. Accordingly, it is possibleto adjust the viscosity of the thermosetting resin composition (C) byblending the epoxy resin containing the reaction product having adesired viscosity as the epoxy resin to be contained in thethermosetting resin composition (C) of the present invention.

These epoxy resins may be used singly or two or more kinds of thereofmay be used concurrently.

In the case of concurrently using two or more kinds of these epoxyresins, it is preferable to use an epoxy resin which is liquid at roomtemperature and an epoxy resin which is solid at room temperature incombination in order to adjust the viscosity of the thermosetting resincomposition (C) to a viscosity range in which the shape of the prepregcan be maintained.

The content of the epoxy resin which is liquid at room temperature in100 parts by mass of the epoxy resin (A) is preferably from 10 to 90parts by mass, more preferably from 15 to 90 parts by mass, and stillmore preferably from 20 to 90 parts by mass.

It is preferable to set the viscosity of the thermosetting resincomposition (C) to a proper range by setting the content of the epoxyresin which is liquid at room temperature in 100 parts by mass of theepoxy resin (A) to the above range.

Examples of commercially available products of the epoxy resin which isliquid at room temperature may include bisphenol A type epoxy resinssuch as jER 825, 826, 827, 828, and 834 (all manufactured by MitsubishiChemical Corporation), EPICLON (registered trademark) 850 (manufacturedby DIC Corporation), Epototo (registered trademark) YD-128 (manufacturedby NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.), DER-331 and DER-332(manufactured by The Dow Chemical Company), and ARALDITE (registeredtrademark) LY 556 (manufactured by Huntsman Advanced Materials LLC);

bisphenol F type epoxy resins such as jER 806, 807, and 1750 (allmanufactured by Mitsubishi Chemical Corporation), EPICLON (registeredtrademark) 830 (manufactured by DIC Corporation), and Epototo(registered trademark) YD-170 and Epototo (registered trademark) YD-175(all manufactured by NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.);

phenol novolak type epoxy resins such as jER 152 (manufactured byMitsubishi Chemical Corporation), EPICLON (registered trademark) N-730A(manufactured by DIC Corporation), and DEN-425 (manufactured by The DowChemical Company);

amine type epoxy resins such as jER 604 and 630 (all manufactured byMitsubishi Chemical Corporation) and MY 0600 and MY 0500 (allmanufactured by Huntsman Advanced Materials LLC); and

alicyclic epoxy resins such as CELLOXIDE 2021P and CELLOXIDE 8000(manufactured by Daicel Corporation).

These epoxy resins which are liquid at room temperature may be usedsingly or two or more kinds thereof may be used concurrently.

As the epoxy resin which is liquid at room temperature, a bisphenol Atype epoxy resin and a phenol novolak type epoxy resin are preferablefrom the viewpoint of an excellent balance between toughness and heatresistance of the cured product.

The content of epoxy resin which is solid at room temperature in 100parts by mass of the epoxy resin (A) is more preferably from 10 to 90parts by mass and still more preferably from 15 to 90 parts by mass.

It is preferable to set the viscosity of the thermosetting resincomposition (C) to a proper range by setting the content of the epoxyresin which is solid at room temperature in 100 parts by mass of theepoxy resin (A) to the above range.

Examples of commercially available products of the epoxy resin which issolid at room temperature may include phenol novolak type epoxy resinssuch as jER 154 and 157S70 (all manufactured by Mitsubishi ChemicalCorporation), and EPICLON (registered trademark) N-770, EPICLON(registered trademark) N-740, and EPICLON (registered trademark) N-775(all manufactured by DIC Corporation);

cresol novolak type epoxy resins such as EPICLON (registered trademark)N-660, EPICLON (registered trademark) N-665, EPICLON (registeredtrademark) N-670, EPICLON (registered trademark) N-673, and EPICLON(registered trademark) N-695 (all manufactured by DIC Corporation) andEOCN-1020, EOCN-102S, and EOCN-104S (all manufactured by Nippon KayakuCo., Ltd.);

bisphenol A type epoxy resins such as jER 1001, 1002, and 1003 (allmanufactured by Mitsubishi Chemical Corporation);

bisphenol F type epoxy resins such as jER 4004P and 4005P (manufacturedby Mitsubishi Chemical Corporation);

trisphenolmethane type epoxy resins such as jER 1032H60 (manufactured byMitsubishi Chemical Corporation);

biphenyl type epoxy resins such YX 4000 and YL6121H (manufactured byMitsubishi Chemical Corporation);

naphthalene type epoxy resins such as HP4700 (manufactured by DICCorporation); dicyclopentadiene type epoxy resins such as HP7200(manufactured by DIC Corporation);

epoxy resins having an oxazolidone ring skeleton such as TSR-400(manufactured by DIC Corporation), DER 858 (manufactured by The DowChemical Company), and AER 4152 (manufactured by Asahi Kasei E-materialsCorporation); and

bisphenol S type epoxy resins such as EXA-1514 and EXA-1517(manufactured by DIC Corporation).

In addition, as the epoxy resin which is solid at room temperature, anepoxy resin having a structure represented by Formula (3) above in themolecule may be used.

By using an epoxy resin having a structure represented by Formula (3)above in the molecule as the epoxy resin which is solid at roomtemperature, the curing time of the thermosetting resin composition (C)can be decreased and a cured product of the thermosetting resincomposition (C) can exhibit high mechanical properties.

These epoxy resins which are solid at room temperature may be usedsingly or two or more kinds thereof may be used concurrently.

The molecular weight of the epoxy resin to be contained in thethermosetting resin composition (C) of the present invention ispreferably from 200 to 3,000 and more preferably from 300 to 2,000.

When the molecular weight of the epoxy resin to be contained in thethermosetting resin composition (C) of the present invention is in theabove range, it is easy to adjust the viscosity of the thermosettingresin composition (C) to a desired value to be described later.

Here, the molecular weight refers to a weight average molecular weightin terms of polystyrene as determined by gel permeation chromatography.

The epoxy equivalent of the epoxy resin contained in the thermosettingresin composition (C) of the present invention is preferably from 50 to1000 g/eq and more preferably from 90 to 700 g/eq. It is preferable thatthe weight of the epoxy resin contained in the thermosetting resincomposition (C) of the present invention per epoxy equivalent is in theabove range since the crosslinked structure of a cured product of thethermosetting resin composition (C) is uniform.

Here, epoxy equivalent means the molecular weight of the epoxy resin perone epoxy group.

It is preferable that the epoxy resin to be contained in thethermosetting resin composition (C) of the present invention contains anepoxy resin having a structure represented by Formula (3) above in themolecule or a bisphenol A type epoxy resin.

In addition, it is preferable that the epoxy resin to be contained inthe thermosetting resin composition (C) of the present inventioncontains an epoxy resin having a structure represented by Formula (3)above in the molecule and/or a bisphenol A type epoxy resin. In otherwords, it is preferable that the epoxy resin to be contained in thethermosetting resin composition (C) of the present invention contains anepoxy resin having a structure represented by Formula (3) above in themolecule, it is preferable the epoxy resin contains a bisphenol A typeepoxy resin as another aspect, and it is preferable the epoxy resincontains an epoxy resin having a structure represented by Formula (3)above in the molecule and a bisphenol A type epoxy resin as stillanother aspect.

The content of the epoxy resin in 100 parts by mass of the thermosettingresin composition (C) of the present invention is usually from 60 to 95parts by mass, preferably from 65 to 93 parts by mass, and morepreferably from 70 to 90 parts by mass.

The mechanical properties of a cured product of the thermosetting resincomposition (C) are likely to be maintained high by setting the contentof the epoxy resin to equal to or higher than the lower limit value. Theheat resistance at the time of curing hardly diminishes by setting thecontent of the epoxy resin to equal to or lower than the upper limitvalue.

(Epoxy Resin Curing Agent)

The epoxy resin curing agent to be contained in the thermosetting resincomposition (C) of the present invention contains an imidazole-basedcuring agent 1 which is not encapsulated in a microcapsule and a curingagent 2 which is encapsulated in a microcapsule.

[Imidazole-Based Curing Agent 1]

The imidazole-based curing agent 1 to be contained in the thermosettingresin composition (C) of the present invention is an imidazole compound,and it is contained in the thermosetting resin composition (C) withoutbeing encapsulated in a microcapsule.

The imidazole-based curing agent 1 functions as an epoxy resin curingagent of the epoxy resin to be contained in the thermosetting resincomposition (C) of the present invention. The imidazole-based curingagent 1 can cure the thermosetting resin composition (C) in a short timeby being blended in the thermosetting resin composition (C) incombination with the curing agent 2 which is encapsulated in amicrocapsule and the urea derivative comprised in the epoxy resin curingaccelerator.

In addition, by containing the imidazole-based curing agent 1 in thethermosetting resin composition (C) of the present invention, it ispossible to improve the heat resistance of the cured product.

The structure of the imidazole-based curing agent 1 is not particularlylimited as long as it satisfies the above property, but theimidazole-based curing agent 1 is preferably an imidazole compoundrepresented by the following Formula (1) since this exhibits highstorage stability and the cured product exhibits high heat resistance.

(Where R¹ represents a linear or branched alkyl group having from 1 to 5carbon atoms which may have a substituent, a phenyl group which may havea substituent, a hydrogen atom, or a hydroxymethyl group and R²represents a linear or branched alkyl group having from 1 to 5 carbonatoms, a phenyl group which may have a substituent, or a hydrogen atom).

It is preferable that R¹ represents a linear or branched alkyl grouphaving from 1 to 5 carbon atoms which may have a substituent, a phenylgroup which may have a substituent, or a hydroxymethyl group since theimidazole compound exhibits low solubility in the epoxy resin and highstorage stability. It is still more preferable that R¹ represents amethyl group or a hydroxymethyl group since the imidazole compoundexhibits particularly low solubility in the epoxy resin and theproduction thereof is relatively easy.

It is preferable that R² represents a linear or branched alkyl grouphaving from 1 to 5 carbon atoms which may have a substituent or ahydrogen atom since the imidazole compound reacts with the epoxy resinat a relatively high temperature and a cured product exhibiting highheat resistance is obtained. It is still more preferable that R²represents a methyl group or a hydrogen atom since the production of theimidazole compound is relatively easy.

Examples of the imidazole compound represented by Formula (1) above mayinclude imidazole compounds in which the hydrogen at position 5 in1H-imidazole is substituted with a hydroxymethyl group and the hydrogenat position 2 is substituted with a phenyl group or an alkylphenyl groupsuch as 2-phenyl-4,5-dihydroxymethylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,2-phenyl-4-benzyl-5-hydroxymethylimidazole,2-para-toluyl-4-methyl-5-hydroxymethylimidazole,2-meta-toluyl-4-methyl-5-hydroxymethylimidazole,2-meta-toluyl-4,5-dihydroxymethylimidazole, and2-para-toluoyl-4,5-dihydroxymethylimidazole. Among these,2-phenyl-4,5-dihydroxymethylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,2-para-toluoyl-4-methyl-5-hydroxymethylimidazole,2-meta-toluyl-4-methyl-5-hydroxymethylimidazole,2-meta-toluoyl-4,5-dihydroxymethylimidazole and2-para-toluoyl-4,5-dihydroxymethylimidazole are preferable.

The imidazole-based curing agent 1 may be used singly, or two or morekinds thereof may be used in combination.

The imidazole-based curing agent 1 is usually a crystalline solid undera condition of room temperature (25° C.) and exhibits low solubility inan epoxy resin at 100° C. or lower. Hence, the imidazole-based curingagent 1 is preferably a powder having a volume average particle diameterof 100 μm or less, particularly 20 μm or less.

When the volume average particle diameter of the imidazole-based curingagent 1 is equal to or smaller than the upper limit value, theimidazole-based curing agent 1 is favorably dispersed in thethermosetting resin composition (C) and can accelerate the curingreaction.

Incidentally, the volume average particle diameter can be measured byusing a particle size meter (product name: AEOTRAC SPR Model: 7340manufactured by NIKKISO CO., LTD.), and the value of D50 in the particlesize distribution measured is taken.

The imidazole-based curing agent 1 is particularly preferably2-phenyl-4,5-dihydroxymethylimidazole and2-phenyl-4-methyl-5-hydroxymethylimidazole from the viewpoint ofexhibiting high storage stability and of being able to increase the heatresistance of a cured product of the thermosetting resin composition (C)of the present invention.

Examples of commercially available products of these may include CUREZOL(registered trademark) 2PHZ and 2P4MHZ and 2PHZ-PW and 2P4MHZ-PW offinely pulverized products thereof manufactured by SHIKOKU CHEMICALSCORPORATION, but the examples are not limited thereto.

The content of the imidazole-based curing agent 1 in 100% by mass of thethermosetting resin composition (C) of the present invention ispreferably from 5% to 15% by mass, more preferably from 5% to 13% bymass, and still more preferably from 5% to 10% by mass.

By setting the content of the imidazole-based curing agent 1 to be equalto or higher than the lower limit value, the curability of thethermosetting resin composition (C) is improved and the cured productexhibits high heat resistance. It is preferable to set the content ofthe imidazole-based curing agent 1 to be equal to or lower than theupper limit value since it is easy to maintain the mechanical propertiesof a cured product of the thermosetting resin composition (C) high.

[Curing Agent 2 Encapsulated in Microcapsule]

The curing agent 2 which is encapsulated in a microcapsule and is to becontained in the thermosetting resin composition (C) of the presentinvention is not particularly limited as long as it is encapsulated in amicrocapsule, but it is preferably an imidazole derivative having asubstituted imidazole ring in the molecule from the viewpoint of beingeasily microencapsulated and of not impairing the heat resistance of acured product of the thermosetting resin composition (C).

The imidazole derivative is not particularly limited as long as it is acompound which has a function of initiating curing of the thermosettingresin composition (C) at from 70° C. to 110° C., but it is preferably animidazole derivative represented by the following Formula (2).

(Where R³ represents an organic group containing one or more carbonatoms and R⁴ to R⁶ are the same as or different from one another andeach represent a hydrogen atom, a methyl group, or an ethyl group).

Among these, R³ preferably represents a group represented by —CH₂R⁷ or—CH₂OR⁷ (where R⁷ represents an organic group having one or more carbonatoms. Incidentally, the organic group of R⁷ preferably represents ahydrocarbon group which may have a substituent) and particularlypreferably represents a group represented by —CH₂OR⁸ (where R⁸represents an aryl group which may have a substituent).

The curing agent 2 which is encapsulated in a microcapsule is a latentcuring agent which is encapsulated in a microcapsule and cures the epoxyresin to be contained in the thermosetting resin composition (C) of thepresent invention, and the outer layer of the microcapsule is preferablycomposed of a crosslinked polymer.

As the curing agent 2 which is encapsulated in a microcapsule, a masterbatch in which the curing agent 2 which is encapsulated in amicrocapsule is dispersed in an epoxy resin may be used. The epoxy resinserving as a dispersion medium is preferably a bisphenol A type epoxyresin or a bisphenol F type epoxy resin from the viewpoint of stabilityof the microcapsule.

The method for producing the curing agent 2 which is encapsulated in amicrocapsule by encapsulating an imidazole derivative in a microcapsuleis not particularly limited, but it is preferable to use an interfacialpolymerization method, an in situ polymerization method, or a phaseseparation method from an organic solution system from the viewpoint ofuniformity of the shell layer of the microcapsule.

Among the imidazole derivatives, the imidazole derivative represented byFormula (2) above functions as a low temperature curing agent for theepoxy resin and can cure the thermosetting resin composition (C) in ashort time by being blended in the thermosetting resin composition (C)in combination with a urea derivative to be contained in an epoxy resincuring accelerator to be described later.

In addition, in the case of conducting high cycle press molding, theresin composition excessively flows out from the mold in some casesdepending on the structure of the mold since the resin viscositygenerally decreases with an increase in the temperature of the resincomposition.

By containing the curing agent 2 which is encapsulated in a microcapsulein the resin composition as the thermosetting resin composition (C) ofthe present invention, the curing reaction of the resin contained in theresin composition starts at a low temperature, namely, from 70° C. to110° C. and the crosslinking reaction of the thermosetting resincomposition (C) rapidly proceeds during an increase in the resintemperature, namely, from a state in which the resin temperature is aslow as about from 70° C. to 110° C. thus a decrease in the resinviscosity is suppressed and outflow of the resin from the mold can besuppressed. For this reason, the fibers are not exposed by resinwithering or fiber meandering due to excessive flow of resin does notoccur on the surface of a molded body to be obtained but a resin layercan be formed on the surface of the molded body and thus a molded bodyexhibiting favorable molding appearance is likely to be obtained.

Examples of the imidazole derivative represented by Formula (2) abovemay include 1-(2-hydroxy-3-phenoxypropyl)-2-methylimidazole and anadduct compound to be obtained by reacting a glycidyl ether type epoxyresin with 2-methylimidazole.

Among these, an imidazole derivative to be obtained by reacting an arylglycidyl ether type epoxy resin with 2-methylimidazole is preferablesince it can improve the mechanical properties of a cured product of thethermosetting resin composition (C) of the present invention.

The curing agent 2 which is encapsulated in a microcapsule may be usedsingly, or two or more kinds thereof may be used in combination.

The curing agent 2 which is encapsulated in a microcapsule is preferablyone that exhibits heat latent property as well as has a function ofcuring the thermosetting resin composition (C) at 100° C. or lower.Here, the “heat latent property” means a property that the curing agent2 is not reactive with an epoxy resin before a thermal history is giventhereto but it is highly reactive with the epoxy resin even at a lowtemperature after a thermal history has been given thereto at a certaintemperature or higher for a certain time or longer.

Examples of commercially available products of the curing agent 2 whichis encapsulated in a microcapsule may include Novacure (registeredtrademark) HX3721, HX3722, HX3742, and HX3748 manufactured by AsahiKasei E-materials Corporation, which are a curing agent master batchcontaining this, but the examples are not limited thereto.

The content (however, it means the content of the contents encapsulatedin microcapsules including an imidazole derivative but it does notinclude the mass of the microcapsules) of the curing agent 2 which isencapsulated in a microcapsule in 100% by mass of the thermosettingresin composition (C) of the present invention is preferably from 1% to3% by mass, more preferably from 1% to 2.8% by mass, and still morepreferably from 1% to 2.5% by mass.

By setting the content of the curing agent 2 which is encapsulated in amicrocapsule to be equal to or higher than the lower limit value, it iseasy to increase the curing reaction rate of the thermosetting resincomposition (C) and to suppress outflow of the resin composition fromthe mold at the time of curing. By setting the content of the curingagent 2 which is encapsulated in a microcapsule to be equal to or lowerthan the upper limit value, a cured product of the thermosetting resincomposition (C) having a high glass transition temperature is likely tobe obtained.

(Epoxy Resin Curing Accelerator)

The epoxy resin curing accelerator to be contained in the thermosettingresin composition (C) of the present invention contains a ureaderivative.

[Urea Derivative]

The urea derivative to be contained in the thermosetting resincomposition (C) of the present invention functions as a curingaccelerator for the epoxy resin to be contained in the thermosettingresin composition (C) of the present invention and can cure thethermosetting resin composition (C) in a short time by being blended inthe thermosetting resin composition (C) in combination with the curingagent 2 which is encapsulated in a microcapsule.

As the urea derivative, a compound having a dimethyl ureido group ispreferable.

The compound having a dimethyl ureido group is not particularly limitedas long as it generates an isocyanate group and dimethylamine by beingheated at a high temperature and these activate the epoxy group, butexamples thereof may include an aromatic dimethyl urea in which adimethyl ureido group is bonded to an aromatic ring and an aliphaticdimethyl urea in which a dimethyl ureido group is bonded to an aliphaticcompound.

Among these, an aromatic dimethyl urea is preferable from the viewpointof a faster curing rate.

Specific examples thereof may include 3-phenyl-1,1-dimethylurea (PDMU),3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, and2,4-bis(3,3-dimethylureido)toluene (TBDMU). Among these,3-phenyl-1,1-dimethylurea and 2,4-bis(3,3-dimethylureido)toluene arepreferable since these exhibit particularly high curability and furtheraccelerate the curing reaction of the epoxy resin contained in thethermosetting resin composition (C) of the present invention.

The urea derivative may be used singly, or two or more kinds thereof maybe used in combination.

Among the urea derivatives, 3-phenyl-1,1-dimethylurea and2,4-bis(3,3-dimethylureido)toluene described above are usually acrystalline solid under a condition of room temperature (25° C.) andexhibit low solubility in an epoxy resin at 100° C. or lower. Hence, itis preferable that the urea derivative is a powder having a volumeaverage particle diameter of 100 μm or less, particularly 20 μm or less.

When the volume average particle diameter of the urea derivative isequal to or smaller than the upper limit value, the urea derivative canbe favorably dispersed in the thermosetting resin composition (C) andcan accelerate the curing reaction.

Incidentally, the volume average particle diameter can be measured inthe same manner as that for the volume average particle diameter of theimidazole-based curing agent 1 described above.

Examples of commercially available products of 3-phenyl-1,1-dimethylureamay include OMICURE (registered trademark) 94 manufactured by EmeraldPerformance Materials.

Examples of commercially available products of2,4-bis(3,3-dimethylureido)toluene may include OMICURE (registeredtrademark) 24 manufactured by Emerald Performance Materials.

Both of them are not limited to these.

The content of the urea derivative in 100% by mass of the thermosettingresin composition (C) of the present invention is preferably from 2% to5% by mass, more preferably from 2% to 4.5% by mass, still morepreferably from 2% to 4% by mass, particularly preferably from 2% to3.5% by mass, and most preferably from 2% to 3% by mass.

By setting the content of the urea derivative to be equal to or higherthan the lower limit value, it is easy to increase the curing reactionrate of the thermosetting resin composition (C) and to suppress theoutflow of the resin composition from the mold at the time of curing. Bysetting the content of the urea derivative to be equal to or lower thanthe upper limit value, it is easy to maintain high heat resistance of acured product of the thermosetting resin composition (C).

(Arbitrary Components)

In the thermosetting resin composition (C) of the present invention,“other curing agents” which do not correspond to any of theimidazole-based curing agent 1, the curing agent 2 which is encapsulatedin a microcapsule, and the urea derivative may be concurrently used in arange in which the gist of the present invention is not impaired.

However, it is generally required to add only a small amount of “othercuring agents” which exhibit excellent curability at a low temperaturesince the “other curing agents” shorten the life of a resin film formedusing the thermosetting resin composition (C), namely, the period oftime during which the resin film can be stored while maintaining thetackiness and flexibility.

In addition, the thermosetting resin composition (C) of the presentinvention may contain various kinds of additives, resins, fillers andthe like in a range in which the gist of the present invention is notimpaired.

<Prepreg>

The prepreg of the present invention is obtained by impregnating areinforcing fiber substrate with the thermosetting resin composition (C)of the present invention.

(Reinforcing Fiber Substrate)

As the reinforcing fiber substrate, a reinforcing fiber substrate to beused in a usual fiber-reinforced composite material including afiber-reinforced plastic molded body, such as a glass fiber, a carbonfiber, an aramid fiber, or a boron fiber can be used in a usually usedaspect.

As the reinforcing fiber substrate, a glass fiber and a carbon fiber arepreferable, a glass fiber is more preferable as an aspect, and a carbonfiber is more preferable as another aspect.

In addition, as the reinforcing fiber substrate to be contained in theprepreg of the present invention, the same one as a reinforcing fibersubstrate (A) to be described later can be used.

The content of the thermosetting resin composition (C) of the presentinvention in 100% by mass of the prepreg of the present invention ispreferably from 15% to 80% by mass, more preferably from 20% to 60% bymass, and still more preferably from 25% to 45% by mass.

When the content of the thermosetting resin composition (C) of thepresent invention in the prepreg of the present invention is equal to orhigher than the lower limit value, the shape of the prepreg in which thereinforcing fiber substrate (A) is impregnated with the thermosettingresin composition (C) is likely to be maintained. When the content ofthe thermosetting resin composition (C) of the present invention in theprepreg of the present invention is equal to or lower than the upperlimit value, the proportion of reinforcing fibers in the prepreg can bemaintained high and thus the mechanical properties of a compositematerial to be obtained through curing are high.

<Method for Producing Fiber-Reinforced Plastic Molded Body>

The method for producing a fiber-reinforced plastic molded body of thepresent invention is a method for producing a fiber-reinforced plasticmolded body, which includes producing a film laminate (F) by laminatinga resin film formed using a thermosetting resin composition (C) on atleast one surface of a prepreg laminate (E) obtained by laminating aplurality of sheet-like prepreg substrates formed by impregnating areinforcing fiber substrate (A) with a thermosetting resin composition(B) and subjecting the laminate obtained to a heat and pressuretreatment using a mold, and in which the thermosetting resin composition(C) of the present invention is used as the thermosetting resincomposition (C).

In detail, the method for producing a fiber-reinforced plastic moldedbody of the present invention includes the following lamination step andmolding step.

Lamination Step:

A step of producing a film laminate (F) by laminating a resin filmformed using a thermosetting resin composition (C) on at least onesurface of a prepreg laminate (E) obtained by laminating a plurality ofsheet-like prepreg substrates formed by impregnating a reinforcing fibersubstrate (A) with a thermosetting resin composition (B).

Molding Step:

A step of subjecting the laminate obtained to a heat and pressuretreatment using a mold.

Lamination Step:

In the lamination step, a sheet-like prepreg substrate in which areinforcing fiber substrate (A) is impregnated with a thermosettingresin composition (B) and a resin film formed using a thermosettingresin composition (C) are used.

In the lamination step, the resin film is laminated on at least onesurface of a prepreg laminate (E) in which a plurality of sheet-likeprepreg substrates are laminated. In other words, in the productionmethod of the present invention, the resin film may be laminated only onone surface (namely, the surface of one outermost layer) of the prepreglaminate (E) or the resin film may be laminated on both surfaces(namely, the surfaces of both outermost layers) of the prepreg laminate(E).

In the case of laminating the resin film only on one surface of theprepreg laminate (E), a plurality of sheet-like prepreg substrates arelaminated to obtain the prepreg laminate (E) and the resin film isfurther laminated on the surface of the outermost layer of the prepreglaminate (E) to obtain the film laminate (F).

The operation of laminating a plurality of prepreg substrates and theoperation of laminating the prepreg laminate (E) and the resin film maybe conducted outside the mold to be used in the molding step or in themold.

[Film Laminate (F)]

In the film laminate (F) to be used in the present invention, the resinfilm is laminated on at least one surface of the prepreg laminate (E) inwhich a plurality of prepreg substrates are laminated. For example, asillustrated in FIG. 1, a resin film 14 is further laminated on a prepreglaminate (E) 12 in which a plurality of sheet-like prepreg substrates 10are laminated to obtain a film laminate (F) 1.

[Prepreg Substrate]

The prepreg substrate to be used in the present invention is asheet-like prepreg substrate obtained by impregnating the reinforcingfiber substrate (A) with the thermosetting resin composition (B).

The reinforcing fiber constituting the reinforcing fiber substrate (A)is not particularly limited, and for example, an inorganic fiber, anorganic fiber, a metal fiber, and a reinforcing fiber having a hybridconfiguration in which these are combined can be used.

Examples of the inorganic fiber may include a carbon fiber, a graphitefiber, a silicon carbide fiber, an alumina fiber, a tungsten carbidefiber, a boron fiber, and a glass fiber.

Examples of the organic fiber may include an aramid fiber, a highdensity polyethylene fiber, other general nylon fibers, and a polyesterfiber. Examples of the metal fiber may include fibers of stainless steeland iron, and a carbon fiber coated with a metal may also be used. Amongthese, a carbon fiber is preferable when the mechanical properties suchas strength of the fiber-reinforced plastic molded body are taken intoconsideration.

The reinforcing fiber of the reinforcing fiber substrate (A) may be along fiber or a short fiber, and a long fiber is preferable from theviewpoint of excellent rigidity. Examples of a form of the reinforcingfiber substrate may include a form in which a large number of longfibers are aligned in one direction to form a UD sheet (unidirectionalsheet), a form in which long fibers are woven into a cloth material(woven fabric), and a form in which a nonwoven fabric made of shortfibers is formed.

Examples of a method for weaving the cloth material may include plainweave, twill weave, satin weave, and triaxial weave.

The fiber areal weight of the reinforcing fiber substrate (A) ispreferably from 50 to 800 g/m² and more preferably from 75 to 300 g/m².It is preferable that the fiber areal weight of the reinforcing fibersubstrate (A) is equal to or more than the lower limit value of theabove range since the number of laminated layers required for obtaininga molded body having a desired thickness is not great. It is preferablethat the fiber areal weight of the reinforcing fiber substrate (A) isequal to or less than the upper limit value of the above range since itis easy to obtain a prepreg substrate in a favorable impregnated state.

Examples of the thermosetting resin (b1) to be used in the thermosettingresin composition (B) may include an epoxy resin, a vinyl ester resin,an unsaturated polyester resin, a polyimide resin, a maleimide resin,and a phenol resin. In the case of using a carbon fiber as thereinforcing fiber substrate (A), an epoxy resin or a vinyl ester resinis preferable and an epoxy resin is particularly preferable from theviewpoint of adhesive property with the carbon fiber.

The thermosetting resin (b1) may be used singly, or two or more kindsthereof may be used in combination.

It is preferable that the thermosetting resin composition (B) contains acuring agent in addition to the thermosetting resin (b1).

For example, in a case in which the thermosetting resin (b1) is an epoxyresin, the curing agent is not particularly limited but dicyandiamide oran imidazole-based curing agent can be suitably used.

It is preferable that the thermosetting resin composition (B) furthercontains a curing auxiliary in addition to the thermosetting resin (b1)and the curing agent.

For example, in a case in which the thermosetting resin (b1) is an epoxyresin, the curing auxiliary is not particularly limited but a ureacompound can be suitably used.

In addition, the thermosetting resin composition (B) may containadditives such as inorganic fine particles.

The viscosity of the thermosetting resin composition (B) at 30° C. ispreferably from 1.0×10² to 1.0×10⁵ Pa·s, more preferably 5.0×10² to9.8×10⁴ Pa·s, and still more preferably 1.0×10³ to 9.7×10⁴ Pa·s.

When the viscosity of the thermosetting resin composition (B) is equalto or higher than the lower limit value, the prepreg substrate exhibitsexcellent handling properties and work such as fabrication andlamination of the prepreg substrate and molding are facilitated. Whenthe viscosity of the thermosetting resin composition (B) is equal to orlower than the upper limit value, the reinforcing fiber substrate (A) iseasily impregnated with the thermosetting resin composition (B),excessive heating is not required at the time of impregnation, and thedraping property of the prepreg substrate is also hardly impaired.

Examples of the prepreg substrate may include a cloth prepreg substratein which the reinforcing fiber substrate (A) in which reinforcing fibersare woven in the biaxial direction is impregnated with the thermosettingresin composition (B) and a prepreg substrate (UD prepreg substrate) inwhich the reinforcing fiber substrate (A) in which reinforcing fibersare aligned in one direction is impregnated with the thermosetting resincomposition (B). In addition, one in which the reinforcing fibers in theprepreg substrate are shortly cut by making a cut into the prepregsubstrate in which the reinforcing fiber substrate (A) in whichreinforcing fibers are aligned in one direction is impregnated with thethermosetting resin composition (B) may also be used.

The fiber length of the reinforcing fiber in the prepreg substrate ispreferably 12.7 mm or longer and more preferably 25.4 mm or longer. Whenthe fiber length of the reinforcing fiber is equal to or longer than thelower limit value, the mechanical properties of the fiber-reinforcedplastic molded body are likely to be sufficiently high.

The laminated configuration of the prepreg laminate (E) is notparticularly limited. Examples thereof may include a configuration inwhich the respective UD prepreg substrates are laminated so that thefiber axes of the reinforcing fibers of the UD prepreg substratesvertically adjacent to each other are orthogonal to each other in thecase of using a UD prepreg substrate. In the prepreg laminate (E), onlythe same kind of prepreg substrate may be laminated or different kindsof prepreg substrates may be laminated.

The number of laminated prepreg substrates is not particularly limitedand can be appropriately determined according to the properties offiber-reinforced composite material required and the like.

[Resin Film]

The resin film to be used in the present invention is a resin filmformed using the thermosetting resin composition (C) of the presentinvention.

It is preferable that the resin film contains a reinforcing fibersubstrate (D) having a fiber areal weight of 50 g/m² or less.

This makes it possible to further increase the mechanical strength whilesuppressing the generation of molding appearance defects such as resinwithering and fiber meandering on the surface of the fiber-reinforcedplastic molded body.

The reinforcing fiber constituting the reinforcing fiber substrate (D)is not particularly limited, and examples thereof may include the sameones as those mentioned for the reinforcing fiber substrate (A).

The reinforcing fiber substrate (D) is often in a state in which theelongated reinforcing fiber substrate (D) is wound in a roll form andused while being drawn out from that state. In this case, thereinforcing fiber substrate is likely to shrink in the width directionby the tension when being drawn out from the rolled state. As thereinforcing fiber of the reinforcing fiber substrate (D), it ispreferable to use a reinforcing fiber which hardly causes shrinkage ofthe substrate in the width direction even in the case of being drawn outfrom the rolled state and used and exhibits low water absorbingproperty. Specifically, a carbon fiber or a glass fiber is preferable asthe reinforcing fiber of the reinforcing fiber substrate (D).

The reinforcing fiber of the reinforcing fiber substrate (D) may be along fiber or a short fiber.

Examples of the form of the reinforcing fiber substrate (D) may includea form in which a large number of long fibers are aligned in onedirection to form a UD sheet (unidirectional sheet), a form in whichlong fibers are woven into a cloth material (woven fabric), and a formin which a nonwoven fabric are made of short fibers. Among these, anonwoven fabric made of reinforcing fibers is preferable as thereinforcing fiber substrate (D) from the viewpoint of easily obtaining afiber-reinforced plastic exhibiting excellent surface smoothness.

The upper limit value of fiber areal weight of the reinforcing fibersubstrate (D) is 50 g/m², and it is preferably smaller than the fiberareal weight of the reinforcing fiber substrate (A) to be used in theprepreg substrate, more preferably 30 g/m², and still more preferably 15g/m². The lower limit value of the fiber areal weight of the reinforcingfiber substrate (D) is preferably 1 g/m². For example, the fiber arealweight of the reinforcing fiber substrate (D) is preferably from 1 to 50g/m², more preferably from 1 to 30 g/m², and still more preferably from1 to 10 g/m².

When the fiber areal weight of the reinforcing fiber substrate (D) isequal to or more than the lower limit value, the production of thereinforcing fiber substrate (D) is likely to be facilitated. When thefiber areal weight of the reinforcing fiber substrate (D) is equal to orless than the upper limit value, it is easy to suppress a defect thatthe reinforcing fiber substrate (D) is seen through the surface of themolded body.

At the time of molding, the resin contained in the prepreg and resinfilm is allowed to flow and thus the voids are removed.

In a case in which the resin film contains the reinforcing fibersubstrate (D) including a nonwoven fabric, the resin flow at the time ofmolding is suppressed by the reinforcing fiber substrate (D) including anonwoven fabric, but resin flow suppression by the reinforcing fibersubstrate (D) including a nonwoven fabric hardly occurs and the resin islikely to flow when the amount of resin is increased.

Hence, when the fiber areal weight of the reinforcing fiber substrate(D) including a nonwoven fabric is thickened, the resin content in theresin film concomitantly increases but resin withering due to resin flowis likely to occur.

On the other hand, when the resin content in the resin film isrelatively decreased in a case in which the fiber areal weight of thereinforcing fiber substrate (D) including a nonwoven fabric isincreased, resin withering due to shortage of resin is likely to occur.

Accordingly, by setting the fiber areal weight of the reinforcing fibersubstrate (D) including a nonwoven fabric to be equal to or less thanthe upper limit value, it is possible to control the amount of resincontained in the resin film to a proper amount, and as a result, toprevent resin withering at the time of molding and to improve thesurface appearance of the molded body. In addition, it is possible toproperly adjust the thickness of the resin layer remaining on thesurface and to suppress an increase in weight and a decrease in bendingproperty. Furthermore, it is possible to favorably maintain the paintingappearance even in the case of being exposed to a wet heat conditionsince the number of voids remaining in the nonwoven fabric after moldingdecreases.

In a case in which the resin film contains the reinforcing fibersubstrate (D), the fiber length of the reinforcing fiber in the resinfilm is preferably from 5 to 50 mm and more preferably from 10 to 30 mm.

When the fiber length of the reinforcing fiber in the resin film isequal to or longer than the lower limit value, the mechanical propertiesof the fiber-reinforced plastic molded body are likely to besufficiently high. When the fiber length of the reinforcing fiber in theresin film is equal to or shorter than the upper limit value, themoldability of the film laminate (F) is improved.

In a case in which the resin film contains the reinforcing fibersubstrate (D), the fiber volume content rate in the resin film ispreferably 50% by volume or more and more preferably 70% by volume ormore.

When the fiber volume content rate in the resin film is equal to orhigher than the lower limit value, the mechanical properties of thefiber-reinforced plastic molded body are likely to be sufficiently high.

Incidentally, the fiber volume content rate in the resin film means avalue to be measured by the same method as that for the fiber volumecontent rate in the prepreg substrate.

In a case in which the resin film contains the reinforcing fibersubstrate (D), the resin content in the resin film is preferably higherthan that in the reinforcing fiber substrate (D), more preferably from30 to 500 g/m², still more preferably from 40 to 300 g/m², andparticularly preferably from 50 to 150 g/m².

When the resin content in the resin film is equal to or higher than thelower limit, the reinforcing fiber substrate (D) is hardly exposed ontothe surface of the molded body and a fiber-reinforced plastic moldedbody exhibiting excellent surface smoothness is likely to be obtained.When the resin content in the resin film is equal to or lower than theupper limit value, handling of the resin film is likely to befacilitated.

The thickness of the resin film is preferably from 20 to 400 μm and morepreferably from 40 to 300 μm.

When the thickness of the resin film is equal to or thicker than thelower limit value, shielding property of the fiber on the surface of themolded body is excellent. When the thickness of the resin film is equalto or thinner than the upper limit value, the thickness of the moldedbody is less likely to be unnecessarily thick.

The number of the resin films laminated on one surface of the prepreglaminate (E) is not particularly limited, and it may be one or two ormore.

Incidentally, the resin film to be used in the present invention may bea resin film which does not contain the reinforcing fiber substrate (D).

(Molding Step)

In the molding step, the laminate obtained, for example, the filmlaminate (F) obtained in the lamination step is subjected to a heat andpressure treatment using a mold to obtain a fiber-reinforced plasticmolded body.

As a molding method by a heat and pressure treatment using a mold, aknown molding method can be adopted, and examples thereof may includeautoclave molding, oven molding, internal pressure molding, and pressmolding.

In press molding, it is easy to obtain a fiber-reinforced plastic moldedbody having a resin layer formed of a resin film on the surface layerbut the molding pressure is high and the resin tends to flow out of themold as compared to other molding methods. Hence, the present invention,in which outflow of resin from the mold at the time of molding can besuppressed, is more advantageous in the case of adopting press moldingin the molding step and particularly advantageous in the case ofadopting high cycle press molding.

For example, a case in which a film laminate (F) 1 is press molded byusing a mold 100 and which is illustrated in FIG. 2 will be described.

The mold 100 includes a lower mold 110 provided with a convex portion112 on the upper surface side and an upper mold 120 provided with aconcave portion 122 on the lower surface side. When the upper mold 120is brought close to the lower mold 110 to close the mold 100, a cavityhaving a shape complementary to the shape of the intendedfiber-reinforced plastic molded body is formed between the convexportion 112 and the concave portion 122 in the mold 100.

As illustrated in FIG. 2(a), the film laminate (F) 1 is disposed on theconvex portion 112 of the lower mold 110 of the heated mold 100 so thata resin film 14 faces upward.

Subsequently, as illustrated in FIG. 2(b), the upper mold 120 is broughtclose to the lower mold 110 to close the mold 100, and the film laminate(F) 1 is molded by being subjected to a heat and pressure treatment. Thethermosetting resin composition (B) and the thermosetting resincomposition (C) in the laminate 1 cure while flowing by being heatedwhile being pressurized by the mold 100. At this time, excessive flow ofthe thermosetting resin composition (C) is suppressed as the curingagent 2 which is encapsulated in a microcapsule and the urea derivativeare contained in the resin film 14, thus the thermosetting resincomposition (C) is prevented from flowing out from the edge portion ofthe mold 100, and it is possible to prevent excessive outflow of thethermosetting resin composition (C).

After curing, as illustrated in FIG. 2(c), the mold 100 is opened and afiber-reinforced plastic molded body 2 is taken out therefrom.

As the molding conditions, known molding conditions can be adoptedexcept that the laminate contains the thermosetting resin composition(C) of the present invention.

The temperature at the time of molding (the temperature of the mold inthe case of using a mold) is preferably from 100° C. to 180° C. and morepreferably from 120° C. to 160° C.

It is preferable to conduct heating at a temperature equal to or higherthan the lower limit value at the time of molding since it is possibleto conduct curing in a short time and to shorten the molding cycle. Byconducting heating at a temperature equal to or lower than the upperlimit value at the time of molding, resin flow at the time of molding issuppressed and a molded body having favorable appearance is likely to beobtained.

The surface pressure at the time of molding is preferably from 1 to 15MPa and more preferably from 4 to 10 MPa.

By applying a pressure equal to or higher than the lower limit value atthe time of molding, the resin flows and the resin composition spreadsto every corner of the mold and thus a molded body having favorableappearance is likely to be obtained. By applying a pressure equal to orlower than the upper limit value at the time of molding, it is easy toprevent the resin from excessively flowing and the molding appearancefrom deteriorating.

The molding time is preferably from 1 to 15 minutes and more preferablyfrom 2 to 5 minutes.

By conducting molding for a time equal to or longer than the lower limitvalue, it is possible to use a resin composition having excellentstorage stability and/or curability in a short time. By conductingmolding for a time equal to or shorter than the upper limit value, highcycle press molding is possible.

(Shaping Step)

The shaping step is a step of shaping the film laminate (F) obtained inthe lamination step to produce a preform.

In the production method of the present invention, a shaping step may beconducted subsequently to the lamination step, that is, the filmlaminate (F) obtained in the lamination step may be shaped to produce apreform and the preform obtained may be subjected to a molding step as alaminate.

In other words, the production method of the present invention may be amethod in which the lamination step, the shaping step, and the moldingstep are conducted in this order. In this case, the film laminate (F)obtained in the lamination step is shaped in the shaping step to obtaina preform and then the preform obtained is molded by being subjected toa heat and pressure in the molding step to produce a fiber-reinforcedplastic.

The method for shaping the film laminate (F) may be any method as longas it is possible to shape an intermediate shape based on the shape ofthe intended fiber-reinforced plastic molded body, and a known methodcan be adopted except that the film laminate (F) containing thethermosetting resin composition (C) of the present invention is used.

In the method for producing a fiber-reinforced plastic molded body ofthe present invention described above, the film laminate (F) in whichthe resin film formed using the thermosetting resin composition (C) ofthe present invention is laminated on the surface of the prepreglaminate (E) is used. Excessive flow of the thermosetting resincomposition (C) in the mold at the time of molding is suppressed as theimidazole-based curing agent 1 which is not encapsulated in amicrocapsule, the curing agent 2 which is encapsulated in amicrocapsule, and the urea derivative are contained in the resin film.By this, a phenomenon that the thermosetting resin composition (C)contained in the resin film flows out of the mold is suppressed even inthe case of adopting high-cycle press molding. For this reason, thegeneration of molding appearance defects such as resin withering andfiber meandering on the surface of a fiber-reinforced plastic moldedbody to be obtained is suppressed.

In addition, in the method for producing a fiber-reinforced plasticmolded body of the present invention, a resin film is laminated on thesurface of the prepreg laminate (E) and molding is then conducted andthus a defect that the fibers are seen through the surface of afiber-reinforced plastic molded body to be obtained is also suppressed.

[Fiber-Reinforced Plastic Molded Body]

An aspect of the fiber-reinforced plastic molded body of the presentinvention is a cured product of the film laminate (F) obtained in thelamination step or the preform obtained in the shaping step, and thefilm laminate (F) obtained in the lamination step or the preformobtained in the shaping step is molded by being subjected to a heat andpressure treatment as described above.

The fiber-reinforced plastic molded body of the present invention of thepresent aspect includes a composite material portion formed of theprepreg laminate (E) and a resin layer formed of the resin film on thesurface of the composite material portion. The composite materialportion contains a cured product of the reinforcing fiber substrate (A)and the thermosetting resin composition (B), and the resin layercontains a cured product of the thermosetting resin composition (C) ofthe present invention and the reinforcing fiber substrate (D) to be usedif necessary.

For example, as illustrated in FIG. 3, the fiber-reinforced plasticmolded body 2 obtained by molding the film laminate (F) using the mold100 includes a composite material portion 20 formed of a prepreglaminate 12 and a resin layer 22 formed of a resin film 14 on thesurface of the composite material portion 20. The composite materialportion 20 contains a cured product of the reinforcing fiber substrate(A) and the thermosetting resin composition (B). The resin layer 22contains a cured product of the thermosetting resin composition (C) andthe reinforcing fiber substrate (D) to be used if necessary.

The fiber-reinforced plastic molded body 2 illustrated in FIG. 3 has anaspect in which a side portion 4 vertically extends from both ends of aflat plate portion 3 toward the side opposite to the resin layer 22.

In addition, another aspect of the fiber-reinforced plastic molded bodyof the present invention is a cured product of the prepreg of thepresent invention, and the cured product is obtained by laminating aplurality of the prepregs of the present invention if necessary andcuring the laminate by adopting a usual method for curing a prepreg.

The fiber-reinforced plastic molded body of the present invention of thepresent aspect contains a reinforcing fiber substrate and a curedproduct of the thermosetting resin composition (C) of the presentinvention.

Incidentally, when a plurality of the prepregs of the present inventionare laminated, it is possible to adopt the same aspect as that of theprepreg laminate (E) in which a plurality of prepreg substrates arelaminated described above.

The shape and size of the fiber-reinforced plastic molded body of thepresent invention are not particularly limited and can be appropriatelydetermined according to the application.

In the fiber-reinforced plastic molded body of the present invention,excessive flow of the thermosetting resin composition (C) contained inthe resin film at the time of molding is suppressed and thus thegeneration of molding appearance defects such as resin withering andfiber meandering on the surface and a defect that fibers are seenthrough the surface are suppressed.

EXAMPLES

Hereinafter, the present invention will be described in detail withreference to Examples, but the present invention is not limited by theflowing description.

(Measurement of Viscosity of Thermosetting Resin Composition (C))

The viscosity of the thermosetting resin composition (C) was measuredunder the following conditions.

Incidentally, the temperature at which the lowest viscosity is attainedmeans the temperature of the thermosetting resin composition (C) whenthe lowest viscosity is measured in the case of measuring the viscosityby the following method.

Apparatus: Rheometer (“VAR-100” manufactured by TA Instruments)

Plate used: 25 ϕ parallel plate

Plate gap: 0.5 mm

Frequency for measurement: 10 rad/s

Rate of temperature increase: 2.0° C./min

Measurement-started temperature: 30° C.

Stress: 300 Pa

(Measurement of Dynamic Viscoelasticity of Cured Product)

The cured resin plate obtained in the following “Fabrication of curedresin plate” was processed into a test piece (length 55 mm×width 12.5mm), log G′ was plotted with respect to the temperature at a frequencyfor measurement of 1 Hz and a rate of temperature increase of 5° C./minby using a rheometer (ARES-RDA manufactured by TA Instruments), and thetemperature at the intersection point of the approximate straight linein the flat region of log G′ with the approximate straight line in theregion in which log G′ drastically decreases was taken as the glasstransition temperature (G′ Tg) of the cured product to be attained bydynamic viscoelasticity measurement.

[Fabrication of Cured Resin Plate]

The thermosetting resin composition (C) obtained in each example wasinjected between two 4 mm thick glass plates sandwiching a 2 mm thickpolytetrafluoroethylene spacer, heated in a hot air circulating typeconstant temperature oven for 5 minutes under the condition that thetemperature of the surface of the glass plate was 140° C., and thencooled to obtain a cured resin plate.

(Evaluation on Molding Appearance)

The surface on the resin film disposed side of the molded plate obtainedin each example was visually evaluated according to the followingcriteria.

[Evaluation Criteria]

A: Resin withering, fiber meandering, and defect that fibers are seenthrough the surface are not observed.

B: Smoothness of surface is slightly inferior but resin withering, fibermeandering, and lack of hiding of fiber are not observed.

C: Resin withering, fiber meandering, and lack of hiding of fiber arepartially observed.

D: Resin withering, fiber meandering, and lack of hiding of fiber aretotally observed.

(Evaluation on Painting Appearance after Wet Heat Test)

An acrylic urethane black paint was spray painted on the surface on theresin film disposed side of the molded plate obtained in each example soas to have a coating film thickness of about 80 μm. This was held for240 hours under conditions of 50° C. and 95% RH, and the surface of thecoating film was visually evaluated according to the following criteria.

[Evaluation Criteria]

A: Streaky appearance defects are not observed.

B: Streaky appearance defects are observed.

(Raw Materials Used)

The raw materials used in the present Example are presented below.

[Epoxy Resin (c1)]

c1-1: Reaction product of epoxy resin with 4,4′-diaminodiphenylsulfone(produced according to the following “Production of epoxy resin(c1-1)”).

c1-2: Bisphenol A type epoxy resin (product name “jER 828”, weight perepoxy equivalent: 189 manufactured by Mitsubishi Chemical Corporation).

c1-3: Bisphenol S type epoxy resin (product name “EPICLON EXA-1514”,weight per epoxy equivalent: 300 manufactured by DIC Corporation).

c1-4: Phenol novolak type epoxy resin (product name “EPICLON N775”,weight per epoxy equivalent; 189 manufactured by DIC Corporation).

c1-5: Trisphenolmethane type epoxy resin (product name “jER 1032H60”,weight per epoxy equivalent: 169 manufactured by Mitsubishi ChemicalCorporation).

c1-6: Diaminodiphenylmethane type epoxy resin (product name “jER 604”,weight per epoxy equivalent: 120 manufactured by Mitsubishi ChemicalCorporation).

c1-7: Phenol novolak type epoxy resin (product name “jER 152”, weightper epoxy equivalent: 177 manufactured by Mitsubishi ChemicalCorporation).

Production of Epoxy Resin (C1-1)

A bisphenol A type epoxy resin (product name “jER 828” manufactured byMitsubishi Chemical Corporation) and 4,4′-diaminodiphenylsulfone (tradename: SEIKACURE-S manufactured by Wakayama Seika Kogyo Co., Ltd.) weremixed together at a mass ratio of 100:9 at room temperature and mixedand heated at 150° C. to obtain an epoxy resin (c1-1). The epoxy resin(c1-1) is a mixture containing a reaction product of an epoxy resin withan amine compound having at least one sulfur atom in the molecule as amain component (weight per epoxy equivalent: 266 g/eq, viscosity (90°C.): 1.3 Pa·S).

[Imidazole-Based Curing Agent 1]

i-1: 2-Phenyl-4-methyl-5-hydroxymethylimidazole (volume average particlediameter: 3.4 μm, product name “CUREZOL (registered trademark)2P4MHZ-PW” manufactured by SHIKOKU CHEMICALS CORPORATION).

i-2: 2-Phenyl-4,5-dihydroxymethylimidazole (volume average particlediameter: 2.0 μm, product name “CUREZOL (registered trademark) 2PHZ-PW”manufactured by SHIKOKU CHEMICALS CORPORATION).

[Curing Agent 2 Encapsulated in Microcapsule]

h-1: Imidazole-based epoxy resin curing agent master batch (bisphenol Atype epoxy resin: 65% by mass, imidazole derivative (curing agentcomponent) represented by Formula (2) above: 35% by mass, gel time at120° C.: 0.7 minute, product name “Novacure (registered trademark)HX3722” manufactured by Asahi Kasei Corp.).

h-2: Imidazole-based epoxy resin curing agent master batch (bisphenol Atype epoxy resin: 65% by mass, imidazole derivative (curing agentcomponent) represented by Formula (2) above: 35% by mass, gel time at120° C.: 1.1 minutes, product name “Novacure (registered trademark)HX3742” manufactured by Asahi Kasei Corp.).

h-3: Imidazole-based epoxy resin curing agent master batch (bisphenol Atype epoxy resin: 65% by mass, imidazole derivative (curing agentcomponent) represented by Formula (2) above: 35% by mass, gel time at130° C.: 0.5 minute, product name “Novacure (registered trademark)HX3748” manufactured by Asahi Kasei Corp.).

[Urea Derivative]

g-1: 2,4-Bis(3,3-dimethylureido)toluene (TBDMU) (product name “OMICURE24” manufactured by PTI JAPAN).

g-2: 3-Phenyl-1,1-dimethylurea (PDMU) (product name “OMICURE 94”manufactured by PTI JAPAN).

(Fabrication of Master Batch)

The imidazole-based curing agent 1 or the urea derivative was kneadedwith the epoxy resin at the mass ratio presented in Table 1 and thenuniformly dispersed by using a triple roll to fabricate a master batch.

TABLE 1 Master batch I-1 I-2 I-3 I-4 G-1 G-2 Epoxy resin c1-2  Parts bymass 3 3 25 50 1 1 Imidazole-based i-1 Parts by mass 2 8.7 curing agent1 i-2 Parts by mass 2 8.7 Urea derivative g-1 Parts by mass 1 g-2 Pansby mass 1

Example 1

In a dissolving tank, 95 parts by mass of the epoxy resin (c1-1) wasplaced, and the temperature was increased to 60° C., 6 parts by mass ofthe master batch G-2, 10 parts by mass of the curing agent 2 (h-1) whichwas encapsulated in a microcapsule, and 21.8 parts by mass of the masterbatch I-2 were added thereto, and the mixture was further stirred andmixed at 60° C. to obtain a thermosetting resin composition (C) C-1.

For the thermosetting resin composition (C) C-1 obtained, thetemperature at which the lowest viscosity was attained (abbreviated asthe “lowest viscosity temperature” in the table) was measured accordingto the “Measurement of viscosity of thermosetting resin composition(C).”

For the thermosetting resin composition (C) C-1 obtained, the glasstransition temperature (abbreviated as the “glass transition point” inthe table) of the cured product to be attained by dynamicviscoelasticity measurement was also determined according to the“Dynamic viscoelasticity measurement of cured product”.

The results are presented in Table 2.

The thermosetting resin composition (C) C-1 obtained was coated onrelease paper by using a multi coater model M-500 manufactured by HIRANOTECSEED Co., Ltd. to obtain a sheet with release paper having a resincontent of 50 g/m².

The sheet with release paper obtained was laminated so that the releasepaper of the sheet with release paper faced to a glass fiber nonwovenfabric (10 g/m² manufactured by Oji F-Tex Co., Ltd.) and impregnatedunder pressure and the release paper was then peeled off from the sheetto obtain a resin film.

The resin film obtained was disposed on the upper surface of a prepreglaminate (E) in which five Pyrofil prepregs (product name “TR361E250S”manufactured by Mitsubishi Chemical Corporation) were laminated so thatthe fiber axis directions of reinforcing fibers were perpendicular toeach other to obtain a film laminate (F).

The film laminate (F) obtained was cut into 300 mm□300 mm, placed in aflat molding mold of 300 mm square, and press-molded under theconditions of a surface pressure of 7.2 MPa, a mold temperature of 140°C., and a molding time of 5 minutes to obtain a fiber-reinforced plasticmolded body (also referred to as a “molded plate”).

The molded plate obtained was subjected to the evaluation on moldingappearance (abbreviated as the “molding appearance” in the table) andthe evaluation on painting appearance (abbreviated as the “paintingappearance” in the table) after the wet heat test.

The results are presented in Table 2.

Example 2 to Example 7

The thermosetting resin composition (C) C-2 to the thermosetting resincomposition (C) C-7 were prepared in the same manner as in Example 1except that the composition and content of each component were changedas presented in Table 2.

Using the thermosetting resin composition (C) C-2 to thermosetting resincomposition (C) C-7 obtained, the temperature at which the lowestviscosity was attained was measured and the glass transition temperatureof the cured product to be attained by dynamic viscoelasticitymeasurement was determined in the same manner as in Example 1.

In addition, resin films were fabricated and fiber-reinforced plasticmolded bodies (molded plates) were obtained in the same manner as inExample 1 except that the thermosetting resin composition (C) C-2 to thethermosetting resin composition (C) C-7 were used.

The molded plates obtained were subjected to the evaluation on moldingappearance and the evaluation on painting appearance after the wet heattest in the same manner as in Example 1.

The results are presented in Table 2.

Comparative Example 1

A thermosetting resin composition X-1 was prepared in the same manner asin Example 1 except that the master batch I containing theimidazole-based curing agent 1 was not used and the composition andcontent of each component were changed as presented in Table 3.

Using the thermosetting resin composition X-1 obtained, the temperatureat which the lowest viscosity was attained was measured and the glasstransition temperature of the cured product to be attained by dynamicviscoelasticity measurement was determined in the same manner as inExample 1.

In addition, a resin film was fabricated and a fiber-reinforced plasticmolded body (molded plate) was obtained in the same manner as in Example1 except that the thermosetting resin composition X-1 was used.

The molded plate obtained was subjected to the evaluation on moldingappearance and the evaluation on painting appearance after the wet heattest in the same manner as in Example 1.

The results are presented in Table 3.

Comparative Example 2

A thermosetting resin composition X-2 was prepared in the same manner asin Example 1 except that the curing agent 2 which was encapsulated in amicrocapsule was not used and the composition and content of eachcomponent were changed as presented in Table 3.

Using the thermosetting resin composition X-2 obtained, the temperatureat which the lowest viscosity was attained was measured and the glasstransition temperature of the cured product to be attained by dynamicviscoelasticity measurement was determined in the same manner as inExample 1.

In addition, a resin film was fabricated and a fiber-reinforced plasticmolded body (molded plate) was obtained in the same manner as in Example1 except that the thermosetting resin composition X-2 was used.

The molded plate obtained was subjected to the evaluation on moldingappearance in the same manner as in Example 1.

The results are presented in Table 3.

Comparative Example 3

A thermosetting resin composition X-3 was prepared in the same manner asin Example 1 except that the masterbatch G containing a urea derivativewas not used and the composition and content of each component werechanged as presented in Table 3.

Using the thermosetting resin composition X-3 obtained, the temperatureat which the lowest viscosity was attained was measured and the glasstransition temperature of the cured product to be attained by dynamicviscoelasticity measurement was determined in the same manner as inExample 1.

In addition, a resin film was fabricated and a fiber-reinforced plasticmolded body (molded plate) was obtained in the same manner as in Example1 except that the thermosetting resin composition X-3 was used.

The molded plate obtained was subjected to the evaluation on moldingappearance in the same manner as in Example 1.

The results are presented in Table 3.

Incidentally, in the table, the imidazole-based curing agent 1 isabbreviated as the “curing agent 1” and the curing agent 2 which isencapsulated in a microcapsule is abbreviated as the “curing agent 2”.

TABLE 2 Example 1 2 3 4 5 6 7 Epoxy resin c1-1  Parts by mass 95 95 9580 c1-3  Parts by mass 50 c1-4  Parts by mass 50 c1-5  Parts by mass 20c1-6  Parts by mass 20 c1-7  Parts by mass 40 55 Master batch I Epoxyresin c1-2  Parts by mass 13.1 13.1 13.1 50 13.1 13.1 21 Curing agent 1i-1 Parts by mass 8.7 8.7 8.7 14 i-2 Parts by mass 8.7 8.7 8.7 Masterbatch G Epoxy resin c1-2  Parts by mass 3 4 3 3 5 4 3 Urea derivativeg-1 Parts by mass 4 3 5 g-2 Parts by mass 3 3 4 3 Curing agent 2 h-1Parts by mass 10 8 5 10 10 h-2 Parts by mass 8 h-3 Parts by mass 5Content in resin composition Curing agent 1 % by mass 6.6 6.6 6.8 7.16.6 6.5 11.1 Curing agent 2 % by mass 2.6 2.1 1.4 2.3 2.7 2.6 1.4 Ureaderivative % by mass 2.3 3.0 2.3 2.4 3.8 3.0 2.4 Lowest viscositytemperature ° C. 92 95 92 95 97 89 98 Glass transition temperature ° C.158 158 163 169 152 162 173 Molding appearance A B A B B B B Paintingappearance A A A A A A A

TABLE 3 Comparative Example 1 2 3 Epoxy resin c1-1 Parts by mass 95 9575 Master Epoxy resin c1-2 Parts by mass 13.1 25 batch I Curing agent 1 i-2 Parts by mass 8.7 8.7 Master Epoxy resin c1-2 Parts by mass 5 3batch G Urea derivative  g-2 Parts by mass 5 3 Curing agent 2  h-1 Partsby mass 10 10 Content Curing agent 1 % by mass 0 7.1 7.3 in resin Curingagent 2 % by mass 3.0 0 2.9 composition Urea derivative % by mass 4.32.4 0 Lowest viscosity temperature ° C. 88 105 107 Glass transitiontemperature ° C. 141 158 173 Molding appearance B D D Paintingappearance B — —

As presented in Table 2, in Examples 1 to 7 in which resin films formedusing the thermosetting resin compositions (C) C-1 to C-7 of the presentinvention were used, excessive flow of the thermosetting resincompositions (C) C-1 to C-7 at the time of molding was suppressed, theresin withering, fiber meandering, and lack of hiding of fiber were notobserved, and thus molding appearance was excellent. In addition, theglass transition point was 150° C. or higher and thus the paintingappearance after the wet heat test was also excellent.

In Comparative Example 1 in which a resin film formed using thethermosetting resin composition X-1 which did not contain theimidazole-based curing agent 1 was used, the glass transition point waslower than 150° C. and thus the painting appearance after the wet heattest was inferior.

In Comparative Example 2 in which a resin film formed using thethermosetting resin composition X-2 which did not contain the curingagent 2 which was encapsulated in a microcapsule was used andComparative Example 3 in which a resin film formed using thethermosetting resin composition X-3 which did not contain a ureaderivative was used, excessive flow of the thermosetting resincomposition was not sufficiently suppressed and thus the moldingappearance was inferior.

Example 8

A resin film was fabricated and a fiber-reinforced plastic molded body(molded plate) was obtained in the same manner as in Example 1 exceptthat a glass fiber nonwoven fabric (15 g/m² manufactured by Oji F-TexCo., Ltd.) was used instead of the glass fiber nonwoven fabric (10 g/m²manufactured by Oji F-Tex Co., Ltd.).

The molded plate obtained was subjected to the evaluation on moldingappearance and the evaluation on painting appearance after the wet heattest in the same manner as in Example 1.

The results are presented in Table 4.

Example 9

A resin film was fabricated and a fiber-reinforced plastic molded body(molded plate) was obtained in the same manner as in Example 1 exceptthat the resin content in the sheet with release paper was set to 150g/m².

The molded plate obtained was subjected to the evaluation on moldingappearance and the evaluation on painting appearance after the wet heattest in the same manner as in Example 1.

The results are presented in Table 4.

Example 10

A resin film was fabricated and a fiber-reinforced plastic molded body(molded plate) was obtained in the same manner as in Example 1 exceptthat the resin content in the sheet with release paper was set to 75g/m².

The molded plate obtained was subjected to the evaluation on moldingappearance and the evaluation on painting appearance after the wet heattest in the same manner as in Example 1.

The results are presented in Table 4.

TABLE 4 Example Example Example Example 1 8 9 10 Resin Fiber areal g/m²10 15  10 15 film weight of glass fiber nonwoven fabric Resin contentg/m² 50 50 150 75 in sheet with release paper Molding appearance A B A BPainting appearance A A A A

As presented in Table 4, even in the case of fabricatingfiber-reinforced plastic molded bodies using glass fiber nonwovenfabrics having different fiber areal weights and sheets with releasepaper having different resin contents, the molding appearance andpainting appearance after the wet heat test of the fiber-reinforcedplastic molded bodies obtained were both excellent.

INDUSTRIAL APPLICABILITY

According to the present invention, a thermosetting resin composition ofwhich curing can be started at a relatively low temperature in a shorttime and a cured product exhibits high heat resistance and a prepreg tobe obtained by impregnating a reinforcing fiber substrate with thisthermosetting resin composition are provided.

According to the present invention, a molded body which can suppressexcessive flow of the resin at the time of heat and pressure treatment,in which the generation of molding appearance defects such as resinwithering and fiber meandering on the surface and a defect that fibersare seen through the surface are suppressed, and which exhibitsexcellent molding appearance and painting appearance, for example, evenin the case of being subjected to high cycle press molding or beingexposed to a wet heat condition by using a resin film to be obtainedusing the thermosetting resin composition of the present invention, anda method for producing the same are also provided.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 FILM LAMINATE (F)    -   2 FIBER-REINFORCED PLASTIC MOLDED BODY    -   3 FLAT PLATE PORTION    -   4 SIDE PORTION    -   10 PREPREG SUBSTRATE    -   12 PREPREG LAMINATE (E)    -   14 RESIN FILM    -   20 COMPOSITE MATERIAL PORTION    -   22 RESIN LAYER    -   100 MOLD    -   110 LOWER MOLD    -   112 CONVEX PORTION    -   120 UPPER MOLD    -   122 CONCAVE PORTION

1. A film, comprising a thermosetting resin composition, thethermosetting resin composition comprising: an epoxy resin; an epoxyresin curing agent; and an epoxy resin curing accelerator comprising aurea derivative, wherein the epoxy resin curing agent comprises a firstcuring agent which is an imidazole-based curing agent, not beingencapsulated in a microcapsule, and a second curing agent, which isencapsulated in a microcapsule, wherein the film does not comprise areinforcing fiber substrate.
 2. The film of claim 1, wherein theimidazole-based curing agent of the first curing agent is a compound offormula (1):

wherein R¹ is an optionally substituted linear or branched alkyl groupcomprising from 1 to 5 carbon atoms, an optionally substituted phenylgroup, H, or a hydroxymethyl group, and R² is a linear or branched alkylgroup having from 1 to 5 carbon atoms, an optionally substituted phenylgroup, or H, and wherein the second curing agent is a compound offormula (2):

wherein R³ is an organic group comprising a carbon atom and R⁴ to R⁶ areindependently H, a methyl group, or an ethyl group.
 3. The film of claim1, wherein the imidazole-based curing agent of the first curing agent isa compound of formula (1):

wherein R¹ is an optionally substituted linear or branched alkyl groupcomprising from 1 to 5 carbon atoms, an optionally substituted phenylgroup, H, or a hydroxymethyl group, and R² is a linear or branched alkylgroup having from 1 to 5 carbon atoms, an optionally substituted phenylgroup, or H.
 4. The film of claim 1, wherein the urea derivativecomprises 3-phenyl-1,1-dimethylurea or2,4-bis(3,3-dimethylureido)toluene.
 5. The film of claim 1, wherein thefirst curing agent comprises 2-phenyl-4,5-dihydroxymethylimidazole or2-phenyl-4-methyl-5-hydroxymethylimidazole.
 6. The film of claim 1,wherein the second curing agent has a formula (2):

wherein R³ is an organic group comprising a carbon atom, and R⁴ to R⁶are independently H, a methyl group, or an ethyl group.
 7. The film ofclaim 1, wherein the epoxy resin comprises an epoxy resin having astructure unit of formula (3):


8. The film of claim 1, wherein the epoxy resin comprises a bisphenol Atype epoxy resin.
 9. The film of claim 1, wherein, in mass percent, thefirst curing agent is present in a range of from 5 to 15%, the secondcuring agent is present in a range of from 1 to 3%, and the ureaderivative is present in a range of from 2 to 5%, in the thermosettingresin composition.
 10. The film of claim 1, wherein the thermosettingresin composition has a lowest viscosity at from 80° C. to 98° C. intemperature-programmed viscosity measurement to be conducted underconditions of an initial temperature of 30° C. and a rate of temperatureincrease of 2.0° C./min, and wherein the thermosetting resin compositionhas a glass transition temperature of a cured product obtained byheating the thermosetting resin composition at 140° C. for 5 minutesattained by dynamic viscoelasticity measurement of 150° C. or higher.11. The film of claim 1, wherein the content of the thermosetting resincomposition is in a range of from 30 to 150 g/m².
 12. The film of claim1, having a thickness in a range of from 20 to 400 μm.
 13. A method forproducing a fiber-reinforced plastic molded body, the method comprising:preparing a laminate comprising the film of claim 1 and a plurality ofsheet-like prepreg substrates such that the film is arranged on onesurface of the laminate; and subjecting the laminate to a heat andpressure treatment using a mold.
 14. The method of claim 13, furthercomprising: shaping the laminate into a preform before subjecting thelaminate to the heat and pressure treatment.